Dark-winged fungus gnat (Diptera: Sciaridae) maggots
Dark-winged fungus gnat (Diptera: Sciaridae) maggots (fly larvae) are about 3/8 inch long, slender, legless, and have transparent bodies with shiny black head capsules.
Some species of fungus gnat larvae feed on fine roots damaging the plants. However, most larvae feed on decaying plant matter and fungi in the soil and thatch layer. The larvae come to the surface to migrate to pupate.
Fun Fact: Fungus gnat larvae migrate en masse to avoid predation.
For more information about fungus gnats as common houseplant insects, see HGIC 2252, Common Houseplant Insects and Related Pests.